Electrical testing system



June 11, 1940.

Filed Aug. 5, 1937 Patented June 11, 1940 PATENT OFFICE 2,203,878amc'rmcn. rnsrnvo sxs'mrr Albert L. Rosenberg, Oaklyn, N. J., assignorto Radio Corporation of America, a corporation of Delaware ApplicationAugust 5, 1937, Serial No. 157,472

8 Claims.

This invention relates to electrical testing systems such as are usefulin adjusting the electrical constants of high frequency transformers orsimilar devices, and has for its principal object 5 the provision of. animproved apparatus and method of operation whereby successively testeddevices may be rapidly and automatically adjusted to have the sameelectrical characteristics.

v Other objects of the invention are the provision l (1) of an improvedapparatus for automatically adjusting high frequency transformers toresonance at a predetermined frequency, (2) of an improved controlcircuit which responds solely to a change in the value or polarity ofits control potential to effect adjustments of this character,

and (3) of an improved control circuit which responds in one directionto an increase and in the other direction to a decrease of controlpotential regardless of the absolute value or fre- 20 quency of thecontrol potential.

In the manufacture of different types of electrical apparatus such astransformers, capacitors, inductors, wave traps, oscillation generatorsand the like, it is frequently desirable to'utilize sim- 25 ilarcomponent parts which have the same electrical constants.

In the manufacture of. radio receivers, for example, it is desirablethat the coupling transformers be adJusted to resonate at some pre- 30determined frequency. This result is commonly produced by means of ascrew fixed to a molded magnetite transformer core which is so adjustedwith respect to its surrounding coils as to change the inductance ofthese coils to the desired value.

85 Thus, the core adjusting screw is turned in one direction to increasethe coil inductance and the opposite direction to decrease the coilinductance. Similar adjustment is frequently required in many othertypes of apparatus.

l0 In the exemplified embodiment of the invention. such adjustment of atransformer core is effected by means including a reversible motorprovided with a control circuit which functions to (I) produce rotationof the motor in one direclfl tion when the transformer output isincreasing, (2) produce rotation of the motor in the opposite directionwhen the transformer output is decreasing and (3) deenerg'lze the motorwhenthe transformer output attains a constant value. In

50 order that an initial variation in the transformer output may beproduced when the transformer terminals are moved into engagement withthe contacts of the test circuit, the control circuit is also providedwith means for temporarily ener- Io sizing the core adjusting motor toinitiate the automatic operation of the control circuit. While theinvention is illustrated and described as applied to the adjusting ortesting of a coupling transformer, it will be apparent that it isequally applicable to the adjustment of various 5 other types ofapparatus which depend for their adjustment on change in the position ofa core, a plate crotherwise shaped member adapted to produce anelectrical effect.

The invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing and itsscope is indicated by the appended claims.

Referring to the drawing,

Figure 1 is a wiring diagram of. the improved 16 test system, and

Figure 2 illustrates a detail of the relation between the adjustingmotor and the transformer under test.

Aahereinafter explained in greater detail, the 20 illustrated systemincludes a control circuit from which control potential is applied to apair of amplifying channels, one of which operates to maintain onesolenoid-operated switch closed only while the control potential isincreasing and the other of which operates to maintain anothersolenoid-operated switch closed only while the control potential isdecreasing Interconnected with these two solenoids is a relay devicewhich functions to reverse the connections of the adjusting motor sothat the tested device is automatically adjusted to the desiredelectrical condition.

The system includes (1) a test channel which comprises intercoupledamplifiers Ill and II and 5 a detector l2 and (2) a control circuitwhich comprises a pair of amplifiers i3 and H for controlling asolenoid-operated switch l5 and a pair of amplifiers i6 and l! forcontrolling a solenoidoperated switch l8. As hereinafter explained in 0greater detail, the amplifiers i6 and i1 are negatively biased by meansof potential sources 46 and I1 and have their input circuits sointerconnected with the output circuit of the detector I! that thesolenoid I8 is closed when the detector output increases and amplifiersi3 and il are negatively biased by means of potential sources l9 and 20and have their input circuits so interconnected with the output ofdetector I! that the solenoid I5 is closed when the detector outputdecreases.

The transformer 2| to be tested is shown as connected between the outputcircuit 'of ampliher it and the input circuit of amplifier ii. In orderto facilitate ready insertion and removal of the tested transformer 2|,any suitable means 66 may be utilized to establish the desiredconnections. Such means are illustrated as springs or resilientterminals 22 which are fixed at one end and have their other end biasedupwardly and arranged to be pressed downwardly by the transformerterminals 23, the extent of the downward travel of the movable endsbeing determined by means of stops 24 or the like. The transformer core25 to be adjusted is shown diagrammatically as mechanically coupled toan adjusting motor 26.

As shown more particularly in Fig. 2, the core of the transformer 2! isprovided with an adjusting screw 21 arranged to be rotated in eitherdirection by an extension 28 of the shaft of the motor 25.

Also associated with one set of the upwardly biased resilient contacts22 is a switch 29-40 which functions to connect the motor 28 through arelay device 40 to its current supply leads ll for a short interval suchas one second immediately following the connection of the transformer inthe test circuit, this momentary completion of the test motor circuitbeing desirable for producing in the .detector output circuit a changewhich will initiate operation of the motor control circuit. In theoperation of. the switch 28 the contacts 30 move downwardly over thesloped surface of the contacts 29 when the transformer is inserted andmove upwardly over the insulation back of the contact 29 when thetransformer is removed.

It will be observed that the detector output circuit includes resistors32 and 31 and a capacitor 34 and that the control grids of theamplifiers l3 and I6 are connected through lead 35 to the high potentialside of the resistor 33. With these connections, the control grids ofthe amplifiers are subjected to a more positive potential when thedetector output is increasing and to a more negative potential when thedetector output is decreasing. As previously indicated the biaspotentials of the amplifiers are such that the switch 3 closes inresponse to increasing potential and the switch l5 closes in response todecreasing potential.

If the detector output is increasing, current is supplied to thesolenoid which closes the switch i8 thus connecting the supply leads 3|to the motor 26. This motor is operated in one direction until change inthe detector output ceases at resonance for the particular testfrequency applied to the input of the amplifier l0. At the resonantpoint, the solenoid J8 is therefore deenergized, the switch 31 opens andthe motor 26 stops.

If the detector output is decreasing, the switch [5 closes, thusenergizing the operating solenoid 4| of the relay device 40 andoperating the ratchet mechanism 42--43-44--45 one notch in a well knownmanner to reverse the polarity of the connections of the adjusting motor26 to the power supply line 3i and reversing the rotation of the motor.This causes operating current to be supplied to the switch l8 and thetransformer is adjusted to resonance as previously explained. Thisoperation of the motor in the opposite direction continues until changein the detector output ceases when resonance occurs and the solenoidswitch l8 opens, thus stopping the motor 26.

It will be apparent from the foregoing explanation that the inventionprovides a ready means for rapidly and automatically adjustingelectrical devices to a predetermined electrical condition and that itmay assume various forms other than that illustrated and described.

I claim as my invention:

1. The combination of a test channel adapted to receive a device to betested, means for adjusting said device in one direction in response toan increase in the output of said channel and in the opposite directionin response to a decrease in said output, and means responsive to theinsertion of said device in said channel for producing a momentaryinitial variation in said output.

2. The combination of a test channel adapted to receive a. device to betested and provided with an output circuit, means including a capacitorconnected in said output circuit, means responsive to the charging ofsaid capacitor for adjusting said device in one direction, and meansresponsive to the discharge of said capacitor for adjusting said devicein another direction.

3. The combination of a test channel adapted to receive a device to betested and provided with an output circuit, means including a capacitorconnected in said output circuit, means responsive to the charging ofsaid capacitor for adjusting said device in one direction, meansresponsive to the discharging of said condenser for adjusting saiddevice in another direction, and means for producing an initial changein the charge of said capacitor. l

4. The combination of a test channel adapted to receive a transformer tobe tested and provided with an output circuit, means including acapacitor connected in said output circuit, and means responsive tochange in the charge of said capacitor for adjusting the resonance ofsaid channel.

5. The combination of a test channel adapted to receive a transformer tobe tested and provided with an output circuit, means including acapacitor connected in said output circuit, means responsive to changein the charge of said capacitor for adjusting the inductance of saidtransformer to resonance in said channel, and means responsive to theinsertion of said transformer in said channel for producing an initialchange in the charge of said capacitor.

6. The combination of a test channel adapted to receive an electricaldevice to be tested and provided with an output circuit, means forsupplying a signal to said channel, means including a capacitorconnected in said output circuit, and means responsive to change in thecharge of said condenser for adjusting an electrical constant of saiddevice.

'7. The combination of a test channel adapted to receive an electricaldevice to be tested and provided with an output circuit, means forsupplying a signal to said channel, means including a capacitorconnected in said output circuit, and means responsive to change in thecharge of said capacitor for adjusting said device to resonance at thefrequency of said signal.

8. The combination of a test channel provided with an output circuit andadapted to receive an impedance device to be adjusted to resonance insaid channel, impedance means connected in said output circuit, andmeans responsive to the voltage of said impedance means forautomatically adjusting the impedance of said device to resonance insaid channel.

ALBERTL.

